Summary of Memories Change. But Can We Change Them On Purpose?

Overview of Memories Change. But Can We Change Them On Purpose?

This Science Friday interview (hosted by Ira Flatow) features Dr. Steve Ramirez — associate professor of psychology and brain sciences at Boston University and author of How to Change a Memory — discussing how memories are formed, why they change, and how neuroscience is beginning to intentionally manipulate them. The conversation covers basic mechanisms (from molecular to network levels), rodent experiments that activate or alter memories, therapeutic implications (depression, PTSD, neurodegeneration), and Ramirez’s personal reflections on memory and grief.

Key takeaways

• Memories are reconstructive and malleable, not fixed recordings. Recall itself changes a memory.
• Memory formation and recall occur across many levels: gene expression, single-cell structure, populations of cells coordinating, and inter-regional brain rhythms.
• In rodents, researchers can identify and artificially reactivate ensembles of hippocampal cells (engram cells) associated with a memory; activating positive memory engrams can reduce depression-like symptoms.
• Human memory modulation currently relies on noninvasive techniques (recall, therapy, journaling) that already change mood and physiology quickly; invasive, precise (optogenetic-style) control is currently limited to animal models.
• Therapeutic aims include turning down the emotional “volume” of traumatic memories without erasing factual content, and restoring lost memories in neurodegenerative disease by targeting the cells that encode them.
• Ethical concerns and limitations remain: translation from animals to humans, potential misuse, and the complex personal meaning of memories.

How memories work (concise primer)

• Reconstruction not replay: Memory recall is more like rebuilding a scene than playing a stored video; each retrieval can modify the memory.
• Multi-level changes:
  • Molecular: Altered gene expression; sometimes DNA segments are upregulated or edited during memory formation.
  • Cellular: Neurons change anatomy (e.g., dendritic spines) with learning.
  • Network: Ensembles of neurons coordinate activity (like a symphony) to represent memories.
  • Systems: Different brain regions interact and show rhythms during memory processes.
• Functional link to imagination: Brain regions active when recalling the past are often active when imagining the future, suggesting memories are building blocks for prediction.

Memory-manipulation research (what’s been done in animals)

• Engram identification: In rodents, researchers can tag the small subset (~6% in Ramirez’s experiments) of hippocampal neurons active during a particular positive experience.
• Artificial activation: Stimulating those tagged neurons (optogenetics) can re-evoke the positive memory and associated reward-circuit activity.
• Behavioral outcomes: Repeated activation of positive-memory engrams reduced depression-like behaviors in mice, sometimes producing lasting improvement.
• Positive stimuli in experiments: Palatable food (condensed milk/Nutella) or social interaction used as measurable positive experiences.
• Limitations: These tools (e.g., optogenetics, implanted fibers) are invasive and currently applied in animal models.

Therapeutic possibilities and approaches

• Noninvasive human approaches:
  • Guided recall: Asking someone to vividly recall positive experiences can shift mood, physiology, and cognitive flexibility within seconds.
  • Gratitude journaling and structured memory-focused therapies harness the same recall-driven biology and improve well-being.
• Clinical goals:
  • Depression: Amplifying positive memories or their neural correlates could supplement or replace pharmacological therapies.
  • PTSD/trauma: Instead of erasing memories, therapies aim to reduce the debilitating emotional intensity while preserving factual memory and identity.
  • Alzheimer’s/neurodegeneration: Long-term goal is to map memory engrams and “jumpstart” lost memories by targeting the specific cells that encode them.
• Combined methods: A likely path is combining cognitive interventions, pharmacology, and targeted neural interventions.

Personal and human side (Ramirez’s memoir element)

• The book blends science with a memoir of Ramirez’s graduate years and the death of his lab partner Shu Liu.
• Grief shaped his perspective: Loss made him confront the reality that we all become memories, and influenced how he values and interprets personal memories (e.g., the lasting significance of last words or final texts).
• He argues that personal anecdotes give needed context to the human motivations behind scientific work.

Future directions and challenges

• Short-term goal: Create a “Google Maps for memory” — identify cells constituting individual memories, characterize them, and learn to selectively reactivate or protect them.
• Translation timeline: Ramirez expects major progress within a decade (at least in basic mapping and understanding), but translation to safe, precise human interventions will take longer and face technical, ethical, and regulatory hurdles.
• Ethical considerations: Potential for misuse (manipulation of identity or consent), the moral implications of erasing or editing memories, and the social impacts of memory-altering technologies.

Notable quotes and insights

• “Memories are the brain’s best prediction of what actually happened in the past.” — summarizes the constructive/predictive nature of memory.
• “You can’t step in the same river twice” — analogy applied to memory: each recall is unique.
• “In just a few seconds by recalling the best or the worst day of your life you can alter your entire biology.” — emphasizes how quickly memory recall affects physiology.

Practical recommendations for listeners

• Use structured positive-recall practices (e.g., gratitude journaling) to harness memory’s immediate mood- and biology-changing effects.
• Seek therapies that focus on reducing the emotional intensity of traumatic memories (CBT, exposure therapy, emerging reconsolidation treatments) rather than erasure.
• Stay informed about ethical debates as memory-modulation technologies progress; weigh benefits (therapeutic relief) against risks.

Where to learn more

• Steve Ramirez, How to Change a Memory — discussion of the science plus memoir.
• Follow updates in engram research, optogenetics, and human memory reconsolidation studies to track progress toward translational therapies.

Producers and host: Interview on Science Friday with Ira Flatow; Dr. Steve Ramirez (Boston University) is the guest and author cited throughout.